In this work we present a novel technique to estimate the resonance frequency of LC chipless tags (inductor-capacitor parallel circuit) with improved sensitivity and linearity. The developed reader measures the power consumption of a Colpitts oscillator during a frequency sweep. The readout circuit consists of a Colpitts oscillator with a coil antenna, varactor diodes to change the oscillator frequency, analog circuitry to measure the power consumption and a microcontroller to control the whole system and send the data to a PC via USB. When an LC tag is inductively coupled to the oscillator, without contact, a maximum power peak is found. As shown by an experimental calibration using an LC tag made on FR4 substrate, the frequency of this maximum is related to the resonance frequency. Both parameters, power consumption and resonance frequency, present an excellent linear dependence with a high correlation factor (R2 = 0.995). Finally, a screen-printed LC tag has been fabricated and used as relative humidity sensor achieving a sensitivity of (−2.41 ± 0.21) kHz/% with an R2 of 0.946.

中文翻译：

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用于非接触式 LC 传感标签的具有更高灵敏度的读出电路

在这项工作中，我们提出了一种新技术来估计具有改进的灵敏度和线性度的 LC 无芯片标签（电感-电容并联电路）的谐振频率。开发的阅读器在频率扫描期间测量 Colpitts 振荡器的功耗。读出电路由带有线圈天线的 Colpitts 振荡器、用于改变振荡器频率的变容二极管、用于测量功耗的模拟电路和用于控制整个系统并通过 USB 将数据发送到 PC 的微控制器组成。当 LC 标签电感耦合到振荡器时，没有接触，就会发现最大功率峰值。如使用在 FR4 基板上制作的 LC 标签的实验校准所示，该最大值的频率与共振频率有关。两个参数，功耗和谐振频率，呈现出色的线性相关性和高相关系数 (R2 = 0.995)。最后，制造了丝网印刷 LC 标签并用作相对湿度传感器，其灵敏度为 (-2.41 ± 0.21) kHz/%，R2 为 0.946。